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Bonobo (Pan paniscus) spatial memory and communication in a 20-hectare forest

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We used an artificial language as a tool for the study of spatial memory organization in a young Pan paniscus. In the first experiment, we showed the bonobo a road sign just outside its indoor sleeping area. The sign indicated, by means of
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   International Journal of Primatology, Vol. 23, No. 3, June 2002 (  C   2002) Bonobo (  Pan paniscus ) Spatial Memoryand Communication in a 20-hectare Forest Charles R. Menzel, 1,2 E. Sue Savage-Rumbaugh, 1 and Emil W. Menzel Jr. 1 Received November 30, 2000; accepted April 27, 2001 We used an artificial language as a tool for the study of spatial memory or- ganization in a young  Pan paniscus . In the first experiment, we showed thebonoboaroadsignjustoutsideitsindoorsleepingarea.Thesignindicated,bymeans of arbitrarily designated geometrical shapes (lexigrams), where foodwas hidden. Only 2 of the 15 locations were visible from the sign. Distancesranged up to 170 m from the sign. In 99 of 127 test trials the bonobo went directly to the designated location on its first move. In a second experiment,we presented the road sign at varied points in the woods rather than at thesrcinal fixed place. In these trials the goal was a preferred toy. The bonobo’shumancompanionswerenevertoldthelocationofthegoalanddistanceswereup to 650 m. In all 12 trials the bonobo led its companions to the designated place via an efficient path. The bonobo appeared to be able to move, based onthe information provided by a lexigram, from almost any arbitrary startinglocation in its 20-ha environment to any one of the numerous goal locations. KEY WORDS:  spatial cognition; primate; great ape; chimpanzee;  Pan paniscus . This study examines the following questions. How accurately can ayoung symbol-competent male  Pan paniscus  that has been taken into thewoods every day by human companions remember the general layout of a large outdoor environment and the locations of various places where hehas obtained food? How consistently and effectively can he utilize arbitraryroad signs which signal the presence of food or other objects at locations 1 Language Research Center, Georgia State University, 3401 Panthersville Rd., Decatur,Georgia 30034. 2 To whom correspondence should be addressed; e-mail: lrccrm@panther.gsu.edu. 601 0164-0291/02/0600-0601/0  C  2002 Plenum Publishing Corporation  602 Menzel, Savage-Rumbaugh, and Menzel that are not visible at the time of choice? Can he still perform effectivelywhen the road signs and the goal locations are separated by hundreds of meters?Previous studies, including those on ape language, have not examinedhow apes use arbitrary visual signs to discriminate the presence of goalobjects at locations that are at great distances from the sign. Furthermore,we know of no previous study of nonhumans that has clearly shown thatan animal can go from an arbitrary starting location in a forest to any oneof a sizeable number of distant goals. The issue of how flexibly animals canrecall and go to different goals from different starting locations is a basicone in studies of animal spatial learning (Benhamou  et al. , 1990; Boeschand Boesch, 1984; Byrne, 2000; Collett, 1996; Gallistel, 1990, p. 154; Garber,1989, 2000; Janson, 2000; C. Menzel, 1991; E. Menzel, 1973a; R. Menzel, et al. , 1996; Sigg and Stolba, 1981; Woodworth, 1958). For example, Muller et al.  (1996, p. 669) listed “the ability to find a straight-line path between anypair of points in the environment, so that any point can serve as a startinglocation and any other point can serve as a goal” as one of 3 definitive typesof evidence for cognitive maps in animals, the other two types of evidencefor generalized mapping skills being “the capacity to find shortcuts when apath is suddenly opened that is more efficient than the current path” and“theabilitytofindanoptimaldetourwhenamoreefficientrouteissuddenlyblocked” (Muller  et al. , 1996, p. 670).Here,weshallusethecommunicationsystemthatabonobohadlearnedfrom people principally as a tool to examine his spatial memory. We treatquestionsregardinglanguageorcommunicationpersesecondarily.Thatistosay,weshallfocusonthebonoboasareceiverratherthanasasenderofinfor-mation.Elsewherewehaveaddressedquestionsregardingwhether Pan spp.can intentionally use lexigrams (C. Menzel, 1999; Savage-Rumbaugh  et al. ,1986) or can produce other signs (Savage-Rumbaugh  et al. , 1996) to indicatewhere they are going, as well as whether they can read signs produced byothers, and we will not get into these questions here.In the first experiment, we examined whether the bonobo could travelfromhishomebasetoanyoneof15distantgoallocationsonthebasisoftheinformationcontainedinalexigramroadsign.Inthesecondexperiment,westudiedhisabilitytogotodifferentgoalsfromdifferentstartinglocations.Indetail, we examined how effectively the bonobo could perform if he startedout from a random point in familiar terrain and whether he could retain theinformation from a road sign and sustain his motivation and sense of goaldirectionlongenoughtotraveltodestinationsthatwerehundredsofmetersaway and not visible throughout most of the journey. We presented the roadsign (and the bonobo’s starting point) at different locations in the woodsrather than at a single location, and distances ranged up to 650 m.  Bonobo Spatial Memory and Communication 603 METHODSubject The subject was a juvenile male  Pan paniscus , Kanzi, 4 years old at thestart of the experiment. Savage-Rumbaugh  et al.  (1986, 1993) describe hisrearing history and the manner in which he acquired facility in the use of lexigrams. Preliminary Experience Prior to this study, we had not trained Kanzi formally in the use of lexi-grams. He initially began to use lexigrams as an infant after watching exper-imenters try to teach lexigrams to his adoptive mother (Savage-Rumbaugh et al. , 1986, 1993). From 2.5 years of age (beginning 18 mo before this exper-iment) Kanzi had accompanied his human companions daily on excursionsin the 20-ha forest and around the laboratory facilities (Savage-Rumbaugh et al. , 1986). During outings, Kanzi’s human companions had used placenames in spoken English, had pointed toward locations, and had touchedlexigrams on a portable keyboard to announce travel destinations. Kanzi’scompanionshadnotmerelyplacedlexigramsatanamedplace.Instead,theyhad pointed to the lexigrams, talked about them, accompanied their presen-tation with other relevant potential signs, such as photographs, of wherethey were going, and did so at any given point along the trail, whereverappropriate (Savage Rumbaugh  et al. , 1993). Outings had not followed apredetermined route or timetable. If Kanzi indicated an interest in a newdirection, the companions and Kanzi took it. The companions frequentlypointed to and talked about place lexigrams without any travel ensuing.Thus, there had not been any fixed relationship between a caretaker touch-ing a lexigram and the event of moving to that location. Despite the factthat the outings were not structured as formal training sessions, before theonset of this experiment, Kanzi began to select lexigrams corresponding tosites in the woods, and it appeared that he could lead a person to the sitehe had selected, even when the person had no knowledge of the location(Savage-Rumbaugh  et al. , 1986). Apparatus for the First Experiment About 3 m outside the door of the laboratory room in which Kanzi washoused at night, we drove a 1.5-m wooden stake into the ground. On the  604 Menzel, Savage-Rumbaugh, and MenzelFig. 1.  Examples of lexigrams used on the road sign. a)dog pen, b) garden digging plot, c) staff office, d) trailer,e) colony room, f) food. stake was a small board, onto which we hung lexigrams to serve as roadsigns (Fig. 1). Rumbaugh (1977) and Savage-Rumbaugh (1986) describe theprinciples by which lexigrams were srcinally designed. The lexigrams areobviously arbitrary when compared to the signs of distant food sources thatwildbonobosmightemploy,andweassumethattheywouldalsobeneutralormeaninglesstoananimalthatlackedrelevantexperience(suchasKanzihadhad) with them. Most of the test area was heavily forested and moderatelyhilly, and only 2 of the 15 sites that were used in the experiment for theintroduction of food could be seen from where the sign was located. From13 of the 15 food sites it was also impossible to see any other food site. Atall times each of the 15 sites contained an identical insulated cooler, whichserved as a food container. The coolers themselves were never visible fromwhere the sign was located.  Bonobo Spatial Memory and Communication 605 Test Procedure for the First Experiment In the morning and again in the afternoon, for two trials per day, weplaced Kanzi’s rations for that portion of the day inside a food containerat one of the 15 fixed sites. We used the more distant sites less often thancloser ones, and they were not used on very cold or rainy days. Otherwisethe sequence used for site selection was random. We hung 2 lexigrams onthe wooden stake. One of them was FOOD, and the other lexigram corre-sponded to the site that contained food on that occasion, e.g. A-FRAME,SCRUBBY PINE NOOK, PLAY YARD.Kanzi could initiate searching for food at any time by moving to thedoor, or by leading his human companion to the road sign, or by touchingFOOD on the keyboard. The companion accompanied Kanzi to the roadsign and allowed him to lead the way. In a typical trial, as soon as Kanzisaw the road sign he would run 10 m or more ahead of the person, seldomlooking back, and the person had to hurry to keep up with him.Kanzi could visit any number of sites during a trial. Once Kanzi foundand opened the cooler that contained the food, the companion gave him asmall amount of the food and then carried the remainder back to the lab forlater consumption. The companion recorded each station that Kanzi visited.A visit was scored to a station if Kanzi touched the cooler. We conducted127 trials over a 5-mo period.Our aim was to assess what Kanzi had already learned about locationsand about location lexigrams, and how well he could transfer his learning tonew travel problems. Accordingly, the task was novel for Kanzi in severalspecificrespects.First,beforethisexperiment,wehadneverpresentedKanziwith a randomly selected lexigram and then, in addition, required him tolead a person to the corresponding place. Second, we had never restrictedhis daily rations to a single location in the woods and required him to searchfor the single food source. When food was available in the woods in the past,a small amount had been present at each food site. Third, Kanzi had neverencountered a lexigram hung on a post or a lexigram deliberately left in theenvironment as a sign or message that he had to interpret. Fourth, we hadneverrequiredKanzitoleadapersontoanyspecificfoodsitefromastartingpoint near his home cage. We do not intend to imply by these statements,however, that Kanzi brought no relevant experience to the test situation. Analysis of First Experiment We used Monte Carlo (randomization) tests to assess Kanzi’s perfor-mance statistically, that is, to compare his performance to that expected by
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